Ruby Quiz December 2021

Question 1

Express this code using normal array method.

p [“tommy”, “chuckie”].map(&:upcase)

Answer 1

[“tommy”, “chuckie”].map { |name| name.upcase }

[“TOMMY”, “CHUCKIE”]

Question 2

module Sample
  def self.sidekick
    'robin'
  end
end

p Sample.sidekick

Another syntax to call this method?

Answer 2

module Sample
  def self.sidekick
    'robin'
  end
end

p Sample::sidekick

Singleton methods of a module can either be called with dot notation (Batman.sidekick) or :: notation (Batman::sidekick).

Question 3

How to convert “to_boolean” of any value?

Answer 3

s = !! “hello” - double bang

s.class =>TrueClass

Question 4

Which one is correct?

def is_odd(x)
  x % 2 == 0 ? false : true
end

def is_odd(x)
x % 2 != 0
end

Answer 4

Both are correct

Question 5

What are called First-class citizens in the Ruby programming language?

Answer 5

procs can be stored in data structures, passed around as arguments, and returned by methods, thus meeting the definition of a “first-class” language component.

Question 6

What does the following code print?

class Array
  def say_hi
    "HEY!"
  end
end

p [1, “bob”].say_hi

Answer 6

"HEY!"
The Array class was reopened and the say_hi() method was added for all instances of the Array class.

Question 7

What does the following code print? Explain the result.

class Computer
  def initialize
    @sound = "beep beep"
  end

def self.about
“Sometimes I go #{@sound}”
end
end

p Computer.about

Answer 7

“Sometimes I go “

The about() method is a class method and does not have access to the @sound instance variable. @sound is only available to the instance methods, not the class methods. Undefined instance variables have a default value of nil.

What does the following code print?

Question 8

class Xyz
  def paper
    unassigned_local_variable
  end
end

What would be the output?
xyz = Xyz.new
p xyz.paper

Answer 8

This raises an exception and provides the following message: undefined local variable or method `unassigned_local_variable’.

Question 9

What would be the output of the following?

true. class
false. class
nil. class

Answer 9

true. class # TrueClass
false. class # FalseClass
nil. class # NilClass

Question 10

Do you know fixed object_id in Ruby? if so what would be the output of this?

false. object_id
true. object_id
nil. object_id

Answer 10

false. object_id # 0
true. object_id # 20
nil. object_id # 8

Question 11

How you will get the current call stack in Ruby?

Answer 11

def foo
  bar
end
def bar
  puts caller
end
foo

Question 12

What this line will do?

ruby -n -e ‘p eval($_)’

Answer 12

This works because the -n flag does this:

-n assume ‘while gets(); … end’ loop around your script
And $_ is a global variable. Which contains the following:

The last input line of string by gets or readline.

It will act as mini IRB

Question 13

1. object_id => 3
2. object_id=>5
3. object_id=>7

How these ids are generated?

Answer 13

Integer ids use this formula: (number * 2) + 1.

Question 14

queue = []
%w{hello x world}.each do |word|
queue &laquo_space;word and puts “Added to queue” unless word.length < 2
end

puts queue.inspect

is this valid? If so, what is the output?

Answer 14

# Output:
#   Added to queue
#   Added to queue
#   ["hello", "world"]

we can use use ‘and’ and ‘or’ to group operations for single liners

Question 15

How to see the whole Traceback of an exception in Ruby?

Answer 15

def do_division_by_zero; 5 / 0; end
begin
  do_division_by_zero
rescue => exception
  puts exception.backtrace
end

backtrace method